Silicon carbide wafers with relaxed positive bow and related methods

ABSTRACT

Silicon carbide (SiC) wafers and related methods are disclosed that include intentional or imposed wafer shapes that are configured to reduce manufacturing problems associated with deformation, bowing, or sagging of such wafers due to gravitational forces or from preexisting crystal stress. Intentional or imposed wafer shapes may comprise SiC wafers with a relaxed positive bow from silicon faces thereof. In this manner, effects associated with deformation, bowing, or sagging for SiC wafers, and in particular for large area SiC wafers, may be reduced. Related methods for providing SiC wafers with relaxed positive bow are disclosed that provide reduced kerf losses of bulk crystalline material. Such methods may include laser-assisted separation of SiC wafers from bulk crystalline material.

RELATED APPLICATIONS

This application is a continuation of patent application Ser. No.16/415,721, filed on May 17, 2019, now U.S. Pat. No. 10,611,052, thedisclosure of which is hereby incorporated herein by reference in itsentirety.

FIELD OF THE DISCLOSURE

The present disclosure relates to methods for processing crystallinematerials, and more specifically to methods for forming wafers from bulkcrystalline material.

BACKGROUND

Various microelectronic, optoelectronic, and microfabricationapplications require thin layers of crystalline materials as a startingstructure for fabricating various useful systems. Traditional methodsfor cutting thin layers (e.g., wafers) from large diameter crystallineingots of crystalline materials have involved use of wire saws. Wiresawing technology has been applied to various crystalline materials,such as silicon (Si), sapphire, and silicon carbide (SiC). A wire sawtool includes an ultra-fine steel wire (typically having a diameter of0.2 mm or less) that is passed through grooves of one or many guiderollers. Two slicing methods exist, namely, loose abrasive slicing andfixed abrasive slicing. Loose abrasive slicing involves application of aslurry (typically a suspension of abrasives in oil) to a steel wirerunning at high speed, whereby the rolling motion of abrasives betweenthe wire and the workpiece results in cutting of an ingot.Unfortunately, the environmental impact of slurry is considerable. Toreduce such impact, a wire fixed with diamond abrasives may be used in afixed abrasive slicing method that requires only a water-soluble coolantliquid (not a slurry). High-efficiency parallel slicing permits a largenumber of wafers to be produced in a single slicing procedure. FIG. 1illustrates a conventional wire saw tool 1 including parallel wiresections 3 extending between rollers 4A-4C and arranged tosimultaneously saw an ingot 2 into multiple thin sections (e.g., wafers8A-8G) each having a face generally parallel to an end face 6 of theingot 2. During the sawing process, the wire sections 3 supported by therollers 4A-4C may be pressed in a downward direction 5 toward a holder 7underlying the ingot 2. If the end face 6 is parallel to acrystallographic c-plane of the ingot 2, and the wire sections 3 sawthrough the ingot 2 parallel to the end face 6, then each resultingwafer 8A-8G will have an “on-axis” end face 6′ that is parallel to thecrystallographic c-plane.

It is also possible to produce vicinal (also known as offcut or“off-axis”) wafers having end faces that are not parallel to thecrystallographic c-plane. Vicinal wafers (e.g., of SiC) having a 4degree offcut are frequently employed as growth substrates forhigh-quality epitaxial growth of other materials (e.g., AlN and otherGroup III nitrides). Vicinal wafers may be produced either by growing aningot in a direction away from the c-axis (e.g., growing over a vicinalseed material and sawing the ingot perpendicular to the ingotsidewalls), or by growing an ingot starting with an on-axis seedmaterial and sawing the ingot at an angle that departs fromperpendicular to the ingot sidewalls.

Wire sawing of semiconductor materials involves various limitations.Kerf losses based on the width of material removed per cut are inherentto saw cutting and represent a significant loss of semiconductormaterial. Wire saw cutting applies moderately high stress to wafers,resulting in non-zero bow and warp characteristics. Processing times fora single boule (or ingot) are very long, and events like wire breaks canincrease processing times and lead to undesirable loss of material.Wafer strength may be reduced by chipping and cracking on the cutsurface of a wafer. At the end of a wire sawing process, the resultingwafers must be cleaned of debris.

In the case of SiC having high wear resistance (and a hardnesscomparable to diamond and boron nitride), wire sawing may requiresignificant time and resources, thereby entailing significant productioncosts. SiC substrates enable fabrication of desirable power electronic,radio frequency, and optoelectronic devices. SiC occurs in manydifferent crystal structures called polytypes, with certain polytypes(e.g., 4H—SiC and 6H—SiC) having a hexagonal crystal structure.

FIG. 2 is a first perspective view crystal plane diagram showing thecoordinate system for a hexagonal crystal such as 4H—SiC, in which thec-plane ((0001) plane), corresponding to a [0001] (vertical) directionof epitaxial crystal growth) is perpendicular to both the m-plane((1100) plane) and the a-plane ((1120) plane), with the (1100) planebeing perpendicular to the [1100] direction, and the (1120) plane beingperpendicular to the [1120] direction. FIG. 3 is a second perspectiveview crystal plane diagram for a hexagonal crystal, illustrating avicinal plane 9 that is non-parallel to the c-plane, wherein a vector 10(which is normal to the vicinal plane 9) is tilted away from the [0001]direction by a tilt angle β, with the tilt angle β being inclined(slightly) toward the [1120] direction.

FIG. 4A is a perspective view wafer orientation diagram showingorientation of a vicinal wafer 11A relative to the c-plane ((0001)plane), in which a vector 10A (which is normal to a wafer face 9A) istilted away from the [0001] direction by a tilt angle β. This tilt angleβ is equal to an orthogonal tilt (or misorientation angle) β that spansbetween the (0001) plane and a projection 12A of the wafer face 9A. FIG.4B is a simplified cross-sectional view of the vicinal wafer 11Asuperimposed over a portion of an ingot 14A (e.g., an on-axis ingothaving an end face 6A parallel to the (0001) plane) from which thevicinal wafer 11A was defined. FIG. 4B shows that the wafer face 9A ofthe vicinal wafer 11A is misaligned relative to the (0001) plane by thetilt angle β.

FIG. 5 is a top plan view of an exemplary SiC wafer 25 including anupper face 26 (e.g., that is parallel to the (0001) plane (c-plane), andperpendicular to the [0001] direction) and laterally bounded by agenerally round edge 27 (having a diameter D) including a primary flat28 (having a length L_(F)) that is perpendicular to the (1120) plane,and parallel to the [1120] direction. A SiC wafer may include an outersurface that is misaligned with (e.g., off-axis at an oblique anglerelative to) the c-plane.

Due to difficulties associated with making and processing SiC, SiCdevice wafers have a high cost relative to wafers of various othersemiconductor materials. Typical kerf losses obtained from wire sawingSiC are significantly high compared with a thickness of a resultingwafer, taking into account material loss during the sawing process andsubsequently thinning, grinding, or polishing of the wafer after sawing.It has been impractical to slice wafers thinner than about 350 μmconsidering wire sawing and device fabrication issues.

To seek to address limitations associated with wire sawing, alternativetechniques for removing thin layers of semiconductor materials from bulkcrystals have been developed. One technique involving removal of a layerof silicon carbide from a larger crystal is described in Kim et al.,“4H—SiC wafer slicing by using femtosecond laser double pulses,” OpticalMaterials Express 2450, vol. 7, no. 7 (2017). Such technique involvesformation of laser-written tracks by impingement of laser pulses on SiCto induce subsurface damage, followed by adhesion of the crystal to alocking jig and application of tensile force to effectuate fracturealong a subsurface damage zone. Use of the laser to weaken specificareas in the material followed by fracture between those areas reducesthe laser scanning time.

Another separation technique involving formation of laser subsurfacedamage is disclosed by U.S. Pat. No. 9,925,619 to Disco Corporation.Laser subsurface damage lines are formed by movement of a SiC ingot in aforward path, indexing the focal point of the laser, then moving theingot in a backward path, indexing the focal point of the laser, and soon. The formation of laser subsurface damage produces internal cracksextending parallel to a c-plane within an ingot, and ultrasonicvibration is applied to the ingot to introduce fracture.

A similar separation technique involving formation of laser subsurfacedamage is disclosed by U.S. Pat. No. 10,155,323 to Disco Corporation. Apulsed laser beam is supplied to a SiC ingot to form multiple continuousmodified portions each having a 17 μm diameter with an overlap rate of80% in the feeding direction, and the focal point of the laser isindexed, with the modified portion forming step and indexing step beingalternately performed to produce a separation layer in which cracksadjacent to each other in the indexing direction are connected.Thereafter, ultrasonic vibration is applied to the ingot to introducefracture.

Another technique for removing thin layers of semiconductor materialsfrom bulk crystals is disclosed in U.S. Patent Application PublicationNo. 2018/0126484A1 to Siltectra GmbH. Laser radiation is impinged on asolid state material to create a detachment zone or multiple partialdetachment zones, followed by formation of a polymer receiving layer(e.g., PDMS) and cooling (optionally combined with high-speed rotation)to induce mechanical stresses that cause a thin layer of the solid statematerial to separate from a remainder of the material along thedetachment zone(s).

Tools for forming laser subsurface damage in semiconductor materials areknown in the art and commercially available from various providers, suchas Disco Corporation (Tokyo, Japan). Such tools permit laser emissionsto be focused within an interior of a crystalline substrate, and enablelateral movement of a laser relative to the substrate. Typical laserdamage patterns include formation of parallel lines that are laterallyspaced relative to one another at a depth within a crystalline materialsubstrate. Parameters such as focusing depth, laser power, translationspeed, etc. may be adjusted to impart laser damage, but adjustment ofcertain factors involves tradeoffs. Increasing laser power tends toimpart greater subsurface damage that may increase ease of fracturing(e.g., by reducing the stress required to complete fracturing), butgreater subsurface damage increases surface irregularities alongsurfaces exposed by fracturing, such that additional processing may berequired to render such surfaces sufficiently smooth for subsequentprocessing (e.g., for incorporation in electronic devices). Reducinglateral spacing between subsurface laser damage lines may also increaseease of fracturing, but a reduction in spacing between laser damagelines increases the number of translational passes between a substrateand a laser, thereby reducing tool throughput. Additionally, resultsobtained by laser processing may vary within a substrate, depending onlateral or radial position at a particular vertical position, and/ordepending on vertical position of a substrate face relative to itsoriginal growth position as part of an ingot.

Accordingly, the art continues to seek improved methods for parting orremoving relatively thin layers of crystalline material from a substratethat address issues associated with conventional methods.

SUMMARY

Silicon carbide (SiC) wafers and related methods are disclosed thatinclude intentional or imposed wafer shapes that are configured toreduce manufacturing problems associated with deformation, bowing, orsagging of such wafers due to gravitational forces or from preexistingcrystal stress. In certain embodiments, the intentional or imposed wafershapes may comprise SiC wafers with a relaxed positive bow from siliconfaces thereof. In this manner, effects associated with deformation,bowing, or sagging for SiC wafers, and in particular for large area SiCwafers, may be reduced. In certain embodiments, methods for providingSiC wafers with relaxed positive bow are disclosed that provide reducedkerf losses of bulk crystalline material. Such methods may includelaser-assisted separation of SiC wafers from bulk crystalline material.

In one aspect, a crystalline material processing method comprises:providing a bulk crystalline material comprising SiC; and separating aSiC wafer from the bulk crystalline material such that the SiC waferforms a relaxed positive bow from a silicon face of the SiC wafer, and akerf loss associated with forming the SiC wafer from the bulkcrystalline material is less than 250 microns (μm). In certainembodiments, the kerf loss is less than 175 μm; or in a range including100 μm to 250 μm. In certain embodiments, the relaxed positive bow is ina range from greater than 0 μm to 50 μm; or in a range from greater than0 μm to 40 μm; or in a range from greater than 0 μm to 15 μm; or in arange including 30 μm to 50 μm; or in a range including 8 μm to 16 μm.In certain embodiments, the SiC wafer comprises a diameter to thicknessratio of at least 250; or at least 300; or at least 400; or in a rangeincluding 250 to 1020. In certain embodiments, the SiC wafer comprisesan n-type conductive SiC wafer; or a semi-insulating SiC wafer; or anunintentionally doped SiC wafer. In certain embodiments, a carbon faceof the SiC wafer comprises a shape that corresponds to the relaxedpositive bow from the silicon face. In certain embodiments, a profile ofthe silicon face that is defined by the relaxed positive bow differsfrom a profile of a carbon face of the SiC wafer.

In another aspect, a crystalline material processing method comprises:providing a bulk crystalline material comprising silicon carbide (SiC);forming a subsurface laser damage pattern within the bulk crystallinematerial; separating a SiC wafer from the bulk crystalline materialalong the subsurface laser damage pattern such that the SiC wafercomprises a relaxed positive bow from a silicon face of the SiC wafer.In certain embodiments, the relaxed positive bow is in a range fromgreater than 0 μm to 50 μm; or in a range from greater than 0 μm to 15μm; or in a range including 30 μm to 50 μm; or in a range including 8 μmto 16 μm. In certain embodiments, forming the subsurface laser damagepattern comprises variably adjusting a laser power across the bulkcrystalline material to form a nonlinear profile of the subsurface laserdamage pattern such that the relaxed positive bow is provided afterseparation. In certain embodiments, forming the subsurface laser damagepattern comprises variably adjusting a focal point of a laser across thebulk crystalline material to form a nonlinear profile of the subsurfacelaser damage pattern such that the relaxed positive bow is providedafter separation. In certain embodiments, the bulk crystalline materialis arranged with a radial doping profile such that laser absorptionduring said forming the subsurface laser damage pattern forms anonlinear profile of the subsurface laser damage pattern such that therelaxed positive bow is provided after separation. In certainembodiments, the SiC wafer comprises a diameter to thickness ratio of atleast 250; or at least 300; or at least 400; or in a range including 250to 1020. In certain embodiments, a kerf loss associated with forming theSiC wafer from the bulk crystalline material is less than 250 microns(μm).

In another aspect, any of the foregoing aspects, and/or various separateaspects and features as described herein, may be combined for additionaladvantage. Any of the various features and elements as disclosed hereinmay be combined with one or more other disclosed features and elementsunless indicated to the contrary herein.

Those skilled in the art will appreciate the scope of the presentdisclosure and realize additional aspects thereof after reading thefollowing detailed description of the preferred embodiments inassociation with the accompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The accompanying drawing figures incorporated in and forming a part ofthis specification illustrate several aspects of the disclosure, andtogether with the description serve to explain the principles of thedisclosure.

FIG. 1 includes a first frame providing a perspective view of an ingotreceived by a conventional wire saw tool and being subjected to a wiresawing process, and a second frame providing a perspective view ofmultiple wafers obtained by the wire sawing process.

FIG. 2 is a first perspective view crystal plane diagram showing thecoordinate system for a hexagonal crystal such as 4H silicon carbide(SiC).

FIG. 3 is a second perspective view crystal plane diagram for ahexagonal crystal, illustrating a vicinal plane that is non-parallel tothe c-plane.

FIG. 4A is a perspective view wafer orientation diagram showingorientation of a vicinal wafer relative to the c-plane.

FIG. 4B is a simplified cross-sectional view of the vicinal wafer ofFIG. 4A superimposed over a portion of an ingot.

FIG. 5 is a top plan view of an exemplary SiC wafer, with superimposedarrows showing crystallographic orientation directions.

FIG. 6A is a side elevation schematic view of an on-axis ingot ofcrystalline material.

FIG. 6B is a side elevation schematic view of the ingot of FIG. 6A beingrotated by 4 degrees, with a superimposed pattern for cutting endportions of the ingot.

FIG. 6C is a side elevation schematic view of an ingot following removalof end portions to provide end faces that are non-perpendicular to thec-direction.

FIG. 7 is a perspective view schematic of a moveable laser toolconfigured to focus laser emissions within an interior of a crystallinematerial to form subsurface damage.

FIGS. 8A and 8B provide exemplary laser tool travel paths relative to acrystalline material for formation of subsurface damage within thecrystalline material, with FIG. 8B including a superimposed arrowshowing orientation of subsurface damage lines relative to the [1120]direction of a hexagonal crystal structure of the crystalline material.

FIG. 9 is a perspective view schematic of the surface structure of anoff-axis (relative to the c-axis) or vicinal 4H—SiC crystal afterfracture but prior to smoothing, with the fractured surface exhibitingterraces and steps.

FIGS. 10A-10D are cross-sectional schematic views of formation ofsubsurface laser damage in a substrate of crystalline material byfocusing laser emissions into a bare substrate, through a surface of asubstrate supported by a carrier, through a carrier and an adhesivelayer into a substrate, and through a carrier into a substrate,respectively.

FIG. 11 is a cross-sectional schematic view of a bulk crystallinematerial including a first subsurface laser damage pattern formedtherein.

FIG. 12 is a cross-sectional schematic view of the bulk crystallinematerial of FIG. 11 following formation of a second subsurface laserdamage pattern that is registered with the first subsurface laser damagepattern, with an overlapping vertical extent of the first and secondsubsurface laser damage patterns.

FIG. 13 is a cross-sectional schematic view of a portion of bulkcrystalline material showing subsurface laser damage with superimposeddashed lines identifying an anticipated kerf loss material region.

FIG. 14 is a cross-sectional schematic view of a portion of the bulkcrystalline material showing curved subsurface laser damage withsuperimposed dashed lines identifying the anticipated kerf loss materialregion.

FIG. 15 is cross-sectional schematic view of laser emissions withvariable laser power being focused across a portion of the bulkcrystalline material to form the curved shape of subsurface laserdamage.

FIG. 16 is cross-sectional schematic view of laser emissions withvariable height adjustment being focused across a portion of the bulkcrystalline material to form the curved shape of subsurface laserdamage.

FIG. 17 is cross-sectional schematic view of laser emissions beingfocused across a variably doped portion of the bulk crystalline materialto form the curved shape of subsurface laser damage.

FIG. 18 is a side cross-sectional schematic view of bulk crystallinematerial of SiC on a seed crystal, showing a cylindrically shaped higherdoping region extending upward from the seed crystal through the entirethickness of the bulk crystalline material along a central portionthereof.

FIG. 19 is a top schematic view of a SiC wafer derived from the bulkcrystalline material of FIG. 18 along a cross-sectional portion.

FIG. 20 is a side cross-sectional schematic view of bulk crystallinematerial of SiC on the seed crystal, showing a frustoconically shapedhigher doping region extending upward from the seed crystal through theentire thickness of the bulk crystalline material along a centralportion thereof.

FIG. 21 is a side cross-sectional schematic view of bulk crystallinematerial of SiC on the seed crystal, showing a frustoconically shapedhigher doping region extending upward from the seed crystal at anon-centered position relative to a center of the seed crystal andupward through the entire thickness of the bulk crystalline material.

FIG. 22 is a side cross-sectional schematic view of a SiC wafer having arelaxed positive bow from a silicon face thereof and a correspondingshape of a carbon face according to embodiments disclosed herein.

FIG. 23 is a side cross-sectional schematic view of a SiC wafer having arelaxed positive bow from a silicon face thereof and a generally planarcarbon face according to embodiments disclosed herein.

FIGS. 24A-24C are side cross-sectional schematic views of a SiC waferduring edge-supported measurements to quantify relaxed positive bowwhile correcting for gravitational effects.

FIG. 25 is a side cross-sectional schematic view of a SiC wafer duringvertically-oriented measurements to quantify relaxed positive bow.

FIG. 26 is a schematic side cross-sectional view of a conventional laserfocusing apparatus that focuses an incoming horizontal beam with a lens,forming an outgoing beam having a beam waist pattern having a minimumwidth at a downstream position corresponding to a focal length of thelens.

FIG. 27 is a schematic side cross-sectional view of a verticallyoriented focused laser beam exhibiting a beam waist within a crystallinematerial, with illustration of decomposition threshold points atdifferent vertical positions relative to the beam waist.

DETAILED DESCRIPTION

The embodiments set forth below represent the necessary information toenable those skilled in the art to practice the embodiments andillustrate the best mode of practicing the embodiments. Upon reading thefollowing description in light of the accompanying drawing figures,those skilled in the art will understand the concepts of the disclosureand will recognize applications of these concepts not particularlyaddressed herein. It should be understood that these concepts andapplications fall within the scope of the disclosure and theaccompanying claims.

It will be understood that, although the terms first, second, etc. maybe used herein to describe various elements, these elements should notbe limited by these terms. These terms are only used to distinguish oneelement from another. For example, a first element could be termed asecond element, and, similarly, a second element could be termed a firstelement, without departing from the scope of the present disclosure. Asused herein, the term “and/or” includes any and all combinations of oneor more of the associated listed items.

It will be understood that when an element such as a layer, region, orsubstrate is referred to as being “on” or extending “onto” anotherelement, it can be directly on or extend directly onto the other elementor intervening elements may also be present. In contrast, when anelement is referred to as being “directly on” or extending “directlyonto” another element, there are no intervening elements present.Likewise, it will be understood that when an element such as a layer,region, or substrate is referred to as being “over” or extending “over”another element, it can be directly over or extend directly over theother element or intervening elements may also be present. In contrast,when an element is referred to as being “directly over” or extending“directly over” another element, there are no intervening elementspresent. It will also be understood that when an element is referred toas being “connected” or “coupled” to another element, it can be directlyconnected or coupled to the other element or intervening elements may bepresent. In contrast, when an element is referred to as being “directlyconnected” or “directly coupled” to another element, there are nointervening elements present.

Relative terms such as “below” or “above” or “upper” or “lower” or“horizontal” or “vertical” may be used herein to describe a relationshipof one element, layer, or region to another element, layer, or region asillustrated in the Figures. It will be understood that these terms andthose discussed above are intended to encompass different orientationsof the device in addition to the orientation depicted in the Figures.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of the disclosure.As used herein, the singular forms “a,” “an,” and “the” are intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprises,”“comprising,” “includes,” and/or “including” when used herein specifythe presence of stated features, integers, steps, operations, elements,and/or components, but do not preclude the presence or addition of oneor more other features, integers, steps, operations, elements,components, and/or groups thereof.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this disclosure belongs. It willbe further understood that terms used herein should be interpreted ashaving a meaning that is consistent with their meaning in the context ofthis specification and the relevant art and will not be interpreted inan idealized or overly formal sense unless expressly so defined herein.

Silicon carbide (SiC) wafers and related methods are disclosed thatinclude intentional or imposed wafer shapes that are configured toreduce manufacturing problems associated with deformation, bowing, orsagging of such wafers due to gravitational forces or from preexistingcrystal stress. In certain embodiments, the intentional or imposed wafershapes may comprise SiC wafers with a relaxed positive bow from siliconfaces thereof. In this manner, effects associated with deformation,bowing, or sagging for SiC wafers, and in particular for large area SiCwafers, may be reduced. In certain embodiments, methods for providingSiC wafers with relaxed positive bow are disclosed that provide reducedkerf losses of bulk crystalline material. Such methods may includelaser-assisted separation of SiC wafers from bulk crystalline material.

In this manner, processing techniques are disclosed that provide SiCwafers with intentional or imposed shapes while also providing reducedkerf losses compared with conventional wafer separation and shapingprocesses.

As used herein, a “substrate” refers to a crystalline material, such asa single crystal semiconductor material, optionally comprising an ingotor a wafer. In certain embodiments, a substrate may have sufficientthickness (i) to be surface processed (e.g., lapped and polished) tosupport epitaxial deposition of one or more semiconductor materiallayers, and optionally (ii) to be free-standing if and when separatedfrom a rigid carrier. In certain embodiments, a substrate may have agenerally cylindrical or circular shape, and/or may have a thickness ofat least about one or more of the following thicknesses: 200 microns(μm), 300 μm, 350 μm, 500 μm, 750 μm, 1 millimeter (mm), 2 mm, 3 mm, 5mm, 1 centimeter (cm), 2 cm, 5 cm, 10 cm, 20 cm, 30 cm, or more. Incertain embodiments, a substrate may include a thicker wafer that isdivisible into two thinner wafers. In certain embodiments, a substratemay be part of a thicker substrate or wafer having one or more epitaxiallayers (optionally in conjunction with one or more metal contacts)arranged thereon as part of a device wafer with a plurality ofelectrically operative devices. The device wafer may be divided inaccordance with aspects of the present disclosure to yield a thinnerdevice wafer and a second thinner wafer on which one or more epitaxiallayers (optionally in conjunction with one or more metal contacts) maybe subsequently formed. In certain embodiments, a substrate may comprisea diameter of 150 mm or greater, or 200 mm or greater. In certainembodiments, a substrate may comprise 4H—SiC with a diameter of 150 mm,200 mm, or greater, and a thickness in a range of 100 to 1000 μm, or ina range of 100 to 800 μm, or in a range of 100 to 600 μm, or in a rangeof 150 to 500 μm, or in a range of 150 to 400 μm, or in a range of 200to 500 μm, or in any other thickness range or having any other thicknessvalue specified herein. In certain embodiments, the terms “substrate”and “wafer” may be used interchangeably as a wafer is typically used asa substrate for semiconductor devices that may be formed thereon. Assuch, a substrate or a wafer may refer to free-standing crystallinematerial that has been separated from a larger or bulk crystallinematerial or substrate.

As used herein, “kerf loss” refers to a total amount of material lossassociated with forming an individual wafer from bulk crystallinematerial. The kerf loss may be based on the total width or height ofmaterial removed from the bulk crystalline material subtracted by afinal thickness of the resulting wafer. The kerf loss may be associatedwith the separation process of a wafer from bulk crystalline materialand with subsequent processing steps applied to the wafer, includinggrinding or polishing one or more of the wafer surfaces.

As used herein, “positive bow” for a wafer generally refers to a shapethat curves, bows, or warps outward from a device face of the wafer,e.g., a convex shape from the device face. As also used herein, a“relaxed positive bow” refers to a positive bow of a wafer that isestablished while any bending of the wafer due to gravitational forcesis ignored. A SiC wafer generally forms a silicon face that opposes acarbon face, with a wafer thickness formed therebetween. In manysemiconductor applications, devices are typically formed on the siliconface of the SiC wafer. Wafer bowing, warping, and the like occurs whenone or more of the silicon face and the carbon face form surfacedeviation from a reference plane. As such, positive bow or relaxedpositive bow for a SiC wafer generally refers to a shape that curves,bows, or warps outward from the silicon face of the SiC wafer, e.g. aconvex shape from the silicon face. In certain embodiments, a shape ofthe carbon face may correspond to a positive bow or relaxed positive bowof the silicon face of the SiC wafer. In other embodiments, only thesilicon face may form a positive bow or a relaxed positive bow.

Wafers for semiconductor applications may be subjected to many differentsemiconductor device fabrication techniques for forming devices thereon.One such fabrication technique is epitaxial growth of thin films to formdevice structures, including chemical vapor deposition and metal organicchemical vapor deposition, among others. During epitaxial growth, wafersare typically supported on a susceptor within a growth chamber. Thechamber and susceptor are heated to an appropriate temperature such thatdeposition of thin films occurs on the wafers from decomposed sourcegases within the growth chamber. During growth, a wafer may be supportedin an individual pocket of the susceptor. In particular, the susceptormay provide an edge-supported configuration within the pocket where awafer is supported by multiple points along a perimeter of the wafer.This configuration provides separation between middle portions of thewafer and a bottom surface of the susceptor that is within the pocket.For larger diameter wafers (e.g., 150 mm or above in certainembodiments) with relatively thin thicknesses (e.g., 800 μm and below),gravitational forces and/or various operating conditions may cause thewafer to sag or otherwise deform toward the bottom surface of thesusceptor pocket during processing. In this manner, sagging of the waferforms a variable distance between the wafer and the susceptor, therebycreating an uneven temperature profile across the wafer duringdeposition that can contribute to non-uniform growth of thin filmsthereon. Additionally, other temperature related steps during epitaxy,including cleaning and sublimation steps may also be impacted by wafersagging.

According to embodiments disclosed herein, SiC wafers and relatedmethods for providing SiC wafers are provided with intentional orimposed shapes that are configured to reduce manufacturing problemsassociated with deformation or sagging of wafers that may occur fromgravitational forces or from preexisting crystal stress within thewafer. The imposed shapes may comprise a SiC wafer with a relaxedpositive bow from the silicon face. For epitaxial growth applications,the silicon face of the SiC wafer may therefore be configured toinitially curve away from a susceptor and subsequent sagging of thewafer may position the silicon face to have a more planar configurationwith the susceptor during growth, thereby improving uniformity ofepitaxial layers grown thereon. In certain embodiments, a method ofseparating a SiC wafer from a bulk crystalline material comprisesforming laser subsurface damage within the bulk crystalline material andsubsequently separating the SiC wafer from the bulk crystalline materialalong the laser subsurface damage. In certain embodiments, the shape ofthe resulting SiC wafer is at least partially determined by the shape ofthe laser subsurface damage region formed. For example, laser subsurfacedamage may be provided in a curved manner within the bulk crystallinematerial such that when separated, the wafer is formed with a relaxedpositive bow from the silicon face. In this manner, processingtechniques are disclosed that provide SiC wafers with intentional orimposed shapes while also providing reduced kerf losses compared withconventional wafer separation and shaping processes.

Methods disclosed herein may be applied to substrates or wafers ofvarious crystalline materials, of both single crystal andpolycrystalline varieties. In certain embodiments, methods disclosedherein may utilize cubic, hexagonal, and other crystal structures, andmay be directed to crystalline materials having on-axis and off-axiscrystallographic orientations. In certain embodiments, methods disclosedherein may be applied to semiconductor materials and/or wide bandgapmaterials. Exemplary materials include, but are not limited to, Si,GaAs, and diamond. In certain embodiments, such methods may utilizesingle crystal semiconductor materials having hexagonal crystalstructure, such as 4H—SiC, 6H—SIC, or Group III nitride materials (e.g.,GaN, AlN, InN, InGaN, AlGaN, or AlInGaN). Various illustrativeembodiments described hereinafter mention SiC generally or 4H—SiCspecifically, but it is to be appreciated that other suitablecrystalline materials may be used. Among the various SiC polytypes, the4H—SiC polytype is particularly attractive for power electronic devicesdue to its high thermal conductivity, wide bandgap, and isotropicelectron mobility. Bulk SiC may be grown on-axis (i.e., with nointentional angular deviation from the c-plane thereof, suitable forforming undoped or semi-insulating material) or off-axis (typicallydeparting from a grown axis such as the c-axis by a non-zero angle,typically in a range of from 0.5 to 10 degrees (or a subrange thereofsuch as 2 to 6 degrees or another subrange), as may be suitable forforming N-doped or highly conductive material). Embodiments disclosedherein may apply to on-axis and off-axis crystalline materials, as wellas doped and unintentionally doped crystalline semiconductor materials.In certain embodiments, crystalline material may include single crystalmaterial. Certain embodiments disclosed herein may utilize on-axis4H—SiC or vicinal (off-axis) 4H—SiC having an offcut in a range of from1 to 10 degrees, or from 2 to 6 degrees, or about 4 degrees.

FIGS. 6A, 6B, and 6C schematically illustrate on-axis and off-axis bulkcrystalline material in the form of ingots that may be utilized withmethods disclosed herein. FIG. 6A is a side elevation schematic view ofan on-axis ingot 15 of crystalline material having first and second endfaces 16, 17 that are perpendicular to the c-direction (i.e., the [0001]direction for a hexagonal crystal structure material such as 4H—SiC).FIG. 6B is a side elevation schematic view of the ingot 15 of FIG. 6Abeing rotated by four degrees, with a superimposed pattern 18 (shown indashed lines) for cutting and removing end portions of the ingot 15proximate to the end faces 16, 17. FIG. 6C is a side elevation schematicview of an off-axis ingot 15A formed from the ingot 15 of FIG. 6B,following removal of end portions to provide new first and second endfaces 16A, 17A that are non-perpendicular to the c-direction. If laseremissions of a first depth are supplied through the end face 16 of theingot 15 to form subsurface laser damage, a carrier (not shown) isjoined to the end face 16, and the ingot 15 is fractured along thesubsurface laser damage, then an on-axis wafer may be formed.Conversely, if laser emissions of a first depth are supplied through theend face 16A of the off-axis ingot 15A to form subsurface laser damage,a carrier (not shown) is joined to the end face 16A, and the ingot 15Ais fractured along the subsurface laser damage, then an off-axis wafermay be formed.

Tools for forming laser subsurface damage in crystalline materials areknown in the art and commercially available from various providers, suchas Disco Corporation (Tokyo, Japan). Such tools permit laser emissionsto be focused within an interior of a crystalline material substrate,and enable lateral movement of a laser relative to the substrate.Typical laser damage patterns in the art include formation of parallellines that are laterally spaced relative to one another at a depthwithin a crystalline substrate. Parameters such as focusing depth, laserpower, translation speed, and subsurface damage line spacing may beadjusted to impart laser damage, but adjustment of certain factorsinvolves tradeoffs. Increasing laser power tends to impart greatersubsurface damage that may enhance ease of fracturing (e.g., by reducingthe stress required to complete fracturing), but greater subsurfacedamage increases surface irregularities along surfaces exposed byfracturing, such that additional processing may be required to rendersuch surfaces sufficiently smooth for subsequent processing (e.g., forincorporation in electronic devices), and the additional processingleads to additional kerf losses. Reducing lateral spacing betweensubsurface laser damage lines may also enhance ease of fracturing, but areduction in spacing between laser damage lines increases the number oftranslational passes between a substrate and a laser, thereby reducingtool throughput.

FIG. 7 is a perspective view schematic of one example of a laser tool 29configured to focus laser emissions within an interior of a crystallinematerial 30 to form subsurface damage 40. The crystalline material 30includes an upper surface 32 and an opposing lower surface 34, and thesubsurface damage 40 is formed in the interior of the crystallinematerial 30 between the upper and lower surfaces 32, 34. Laser emissions36 are focused with a lens assembly 35 to yield a focused beam 38, witha focal point thereof being in the interior of the crystalline material30. Such laser emissions 36 may be pulsed at any suitable frequency(typically in the nanosecond, picosecond, or femtosecond range) and beamintensity, with a wavelength below the bandgap of the crystallinematerial 30 to permit the laser emissions 36 to be focused at a targeteddepth below a surface thereof. At the focal point, the beam size andshort pulse width results in an energy density high enough to result invery localized absorption that forms subsurface damage. One or moreproperties of the lens assembly 35 may be altered to adjust a focalpoint of the focused beam 38 to a desired depth within the crystallinematerial 30. Relative lateral motion (e.g., lateral translation) betweenthe lens assembly 35 and the crystalline material 30 may be effected topropagate the subsurface damage 40 in a desired direction, asschematically illustrated by dashed line 42. Such lateral movement maybe repeated in various patterns, including patterns as describedhereinafter.

FIGS. 8A and 8B provide exemplary laser tool travel paths relative to acrystalline material for formation of subsurface damage within thecrystalline material. In certain embodiments, a laser tool portion(e.g., including a lens assembly) may be configured to move while acrystalline material is stationary; in other embodiments, a laser toolportion may be held stationary while a crystalline material is movedrelative to the tool portion. FIG. 8A shows a reversing y-directionlinear scanning movement 46 suitable for forming subsurface damage in apattern of laterally spaced parallel lines within a first crystallinematerial 45A. FIG. 8B shows a y-direction linear scanning movement 48over (and beyond) an entire surface of a second crystalline material 45B(with slight advancement in an x-direction upon each reversal in they-direction), sufficient to form parallel subsurface laser damage linesdistributed through the crystalline material 45B. As shown, the laserdamage lines are perpendicular to the [1120] direction of a hexagonalcrystal structure of the crystalline material 45B along a surface of thecrystalline material 45B, and are and substantially parallel to thesurface of the crystalline material 45B. In certain embodiments,additional subsurface laser damage lines may be interspersed with theparallel subsurface laser damage lines. In other embodiments, variouscombinations and patterns of subsurface laser damage lines andinterspersed subsurface laser damage lines may be provided.

Coverage of an entire surface of a crystalline material with laser linesformed in a y-direction, with unidirectional advancement in anx-direction following each y-direction reversal, may be referred to as asingle pass of laser damage formation. In certain embodiments, laserprocessing of crystalline material to form subsurface damage may beperformed in two, three, four, five, six, seven, or eight passes, or anyother suitable number of passes. Increasing the number of passes atlower laser power can reduce kerf losses. To achieve a desirable balanceof material loss versus process speed, desirable numbers of lasersubsurface damage formation passes have been found to be two to fivepasses, or three to four passes, prior to performance of a fracturingstep.

In certain embodiments, lateral spacing between adjacent lasersubsurface damage lines (whether formed in a single pass or multiplepasses) may be in a range including 80 to 400 μm, or including 100 to300 μm, or including 125 to 250 μm. Lateral spacing between adjacentlaser subsurface damage lines impacts laser processing time, ease offracture, and (depending on c-plane orientation or misorientation)effective laser damage depth.

It has been observed that forming subsurface laser damage lines incrystalline material results in formation of small cracks in theinterior of the material propagating outward (e.g., laterally outward)from the laser damage lines. Such cracks appear to extend substantiallyor predominantly along the c-plane. The length of such cracks appears tobe functionally related to laser power level (which may be calculated asthe product of pulse frequency times energy per pulse). For adjacentlaser subsurface damage lines spaced apart by a specific distance, ithas been observed that increasing laser power in forming such lasersubsurface damage lines tends to increase the ability of cracks toconnect or join between the laser subsurface damage lines, which isdesirable to promote ease of fracturing.

If the crystalline material subject to laser damage formation includesan off-axis (i.e., non c-plane) orientation (e.g., in a range of from0.5-10 degrees, 1-5 degrees, or another misorientation), suchmisorientation may affect desirable laser damage line spacing.

A SiC substrate may include surfaces that are misaligned, e.g., off-axisat an oblique angle relative to the c-plane. An off-axis substrate mayalso be referred to as a vicinal substrate. After fracturing such asubstrate, the as-fractured surface may include terraces and steps(which may be smoothed thereafter by surface processing such as grindingand polishing). FIG. 9 is a perspective view schematic of a surfacestructure of an off-axis 4H—SiC crystal 50 (having an angle A relativeto a c-axis basal plane 56) after fracture but prior to smoothing. Thefractured surface exhibits steps 52 and terraces 54 relative to thec-axis basal plane 56. For a 4 degree off-axis surface, stepstheoretically have a height of about 17 μm for a terrace width of 250μm. For a 4H—SiC crystal having subsurface laser damage, 250 μm spacingbetween laser lines forms terraces of 250 μm width. After fracturing,the stepped surface is subject to being ground smooth, planarized, andpolished in preparation for epitaxial growth of one or more layersthereon.

When subsurface laser damage is formed in crystalline material (e.g.,SiC), and if subsurface laser damage lines are oriented away fromperpendicular to a substrate flat (i.e., non-perpendicular to the [1120]direction), then such laser damage lines extend through multiple stepsand terraces in a manner equivalent to off-axis semiconductor material.For purposes of subsequent discussion, the term “off-axis lasersubsurface damage lines” will be used to refer to laser subsurfacedamage lines that are non-perpendicular to the [1120] direction.

Providing spacing that is too large between adjacent subsurface laserdamage lines inhibits fracture of crystalline material. Providingspacing that is too small between adjacent subsurface laser damage linestends to reduce step heights, but increases the number of verticalsteps, and increasing the number of vertical steps typically requiresgreater separation force to complete fracturing.

Reducing spacing between adjacent laser damage lines to a distance thatis too small may yield diminishing returns and substantially increaseprocessing time and cost. A minimum laser energy threshold is requiredfor SiC decomposition. If this minimum energy level creates connectedcracks between two laser lines spaced about 100 μm apart, then reducinglaser line spacing below this threshold likely offers little benefit interms of reducing kerf loss.

Surface roughness of crystalline material exposed by fracturing canimpact not only subsequent handling such as robot vacuum, but also grindwheel wear, which is a primary consumable expense. Roughness is impactedby both the spacing of subsurface laser damage lines and orientation ofsuch subsurface damage lines relative to the crystal structure of thesemiconductor material. Reducing a gap between subsurface damage linessimply reduces potential step height. Providing off-axis lasersubsurface damage lines tends to break up the long parallel steps thatwould otherwise be present at the laser damage region, and it also helpsmitigate at least some impact from c-plane slope or curvature. When thelaser lines are perpendicular to the flat of a substrate, the cleaveplane parallel to the laser lines along the c-plane extends about 150 mmfrom the flat to the opposing curved end of the wafer. Slight deviationsin the c-plane slope or curvature (which are common for SiC substrates)can create significant variability in the fractured surface as it forcesplane jumping as a fracture propagates. A drawback to providing off-axislaser subsurface damage lines is that such subsurface damage linesgenerally require laser power to be increased to form connected cracksbetween adjacent laser lines. Thus, in certain embodiments, forming acombination of on-axis subsurface laser damage lines (that areperpendicular to the primary flat) and off-axis laser subsurface damagelines provides a good balance between avoiding excessive variability inthe fractured surface without requiring unduly increased laser power toform connected cracks between adjacent laser lines.

In certain embodiments, a laser having a wavelength of 1064 nanometers(nm) may be used to implement methods disclosed herein, with theinventors having gained experience in processing of 4H—SiC. Although awide range of pulse frequencies may be used in certain embodiments,pulse frequencies of 120 kilohertz (kHz) to 150 kHz have beensuccessfully employed. A translation stage speed of 936 millimeters persecond (mm/s) between a laser and a substrate to be processed has beensuccessfully utilized; however, higher or lower translation stage speedsmay be used in certain embodiments with suitable adjustment of laserfrequency to maintain desirable laser pulse overlap. Average laser powerranges for forming subsurface laser damage in doped SiC material are ina range of from 3 watts (W) to 8 W, and 1 W to 4 W for undoped SiCmaterial. Laser pulse energy may be calculated as power divided byfrequency. Laser pulse widths of 3 ns to 4 ns may be used, althoughother pulse widths may be used in other embodiments. In certainembodiments, a laser lens Numerical Aperture (NA) in a range of 0.3 to0.8 may be used. For embodiments directed to processing of SiC, giventhe refractive index change going from air (˜1) to SiC (˜2.6), asignificant change in refractive angle is experienced inside SiCmaterial to be processed, making laser lens NA and aberration correctionimportant to achieving desirable results.

In certain embodiments, a semiconductor material processing method asdisclosed herein may include some or all of the following items and/orsteps. A second carrier wafer may be attached to a bottom side of acrystalline material substrate (e.g., ingot). Thereafter, a top side ofthe crystalline material substrate may be ground or polished, such as toprovide an average surface roughness Ra of less than about 5 nm toprepare the surface for transmitting laser energy. Laser damage may thenbe imparted at a desired depth or depths within the crystalline materialsubstrate, with spacing and direction of laser damage traces optionallybeing dependent on crystal orientation of the crystalline materialsubstrate. A first carrier may be bonded to a top side of thecrystalline material substrate. An identification code or otherinformation linked to the first carrier is associated with a wafer to bederived from the crystalline material substrate. Alternatively, lasermarking may be applied to the wafer (not the carrier) prior toseparation to facilitate traceability of the wafer during and afterfabrication. The crystalline material substrate is then separated orfractured along a subsurface laser damage region to provide a portion ofthe semiconductor material substrate bound to the first carrier, and aremainder of the crystalline material substrate being bound to thesecond carrier. Both the removed portion of the semiconductor materialsubstrate and the remainder of the semiconductor material substrate areground smooth and cleaned as necessary to remove residual subsurfacelaser damage. The removed portion of the semiconductor materialsubstrate may be separated from the carrier. Thereafter, the process maybe repeated using the remainder of the semiconductor material substrate.

In certain embodiments, laser subsurface damage may be formed in acrystalline material substrate prior to bonding the substrate to a rigidcarrier. In certain embodiments, a rigid carrier that is transparent tolaser emissions of a desired wavelength may be bonded to a crystallinematerial substrate prior to subsurface laser damage formation. In suchan embodiment, laser emissions may optionally be transmitted through arigid carrier and into an interior of the crystalline materialsubstrate. Different carrier-substrate subsurface laser formationconfigurations are shown in FIGS. 10A-10D. FIG. 10A is a schematic viewof laser emissions 61 being focused through a surface of a baresubstrate 62 to form subsurface laser damage 63 within the substrate 62,whereby a rigid carrier may be affixed to the substrate 62 followingformation of the subsurface laser damage. FIG. 10B is a schematic viewof laser emissions 61 being focused through a surface of a substrate 62to form subsurface laser damage 63 within the substrate 62, with thesubstrate 62 having previously been bonded using adhesive material 64 toa rigid carrier 66. FIG. 10C is a schematic view of laser emissions 61being focused through a rigid carrier 66 and adhesive 64 to formsubsurface laser damage 63 within a substrate 62 previously bonded tothe rigid carrier 66. In certain embodiments, a surface of the substrate62 distal from the rigid carrier 66 may include one or more epitaxiallayers and/or metallization layers, with the substrate 62 embodying anoperative electrical device prior to formation of the subsurface laserdamage 63. FIG. 10D is a schematic view of laser emissions 61 beingfocused through a rigid carrier 66 into a substrate 62 (without anintervening adhesive layer) to form subsurface laser damage 63 withinthe substrate 62 previously bonded (e.g., via anodic bonding or otheradhesiveless means) to the rigid carrier 66.

In certain embodiments, initial subsurface laser damage centered at afirst depth may be formed within an interior of a crystalline materialsubstrate, and additional subsurface laser damage centered at a seconddepth may be formed within an interior of a substrate, wherein theadditional subsurface laser damage is substantially registered with theinitial subsurface laser damage, and a vertical extent of at least aportion of the additional subsurface laser damage overlaps with avertical extent of at least a portion of the initial laser damage.Restated, one or more subsequent passes configured to impart laserdamage at a different depth may be added on top of one or more priorpasses to provide subsurface laser damage with an overlapping verticalextent. In certain embodiments, addition of overlapping subsurfacedamage may be performed responsive to a determination (e.g., by opticalanalysis) prior to fracturing that one or more prior subsurface laserdamage formation steps were incomplete. Formation of overlappingsubsurface laser damage at different depths may be performed inconjunction with any other method steps herein, including (but notlimited to) formation of multiple interspersed subsurface laser damagepatterns.

FIG. 11 is a cross-sectional schematic view of a bulk crystallinematerial 70 including a first subsurface laser damage pattern 72 formedrelative to a first surface 74 of the bulk crystalline material 70, withthe first subsurface laser damage pattern 72 produced by focusedemissions of a laser 76. The first subsurface laser damage pattern 72 isformed by a plurality of laser damage regions 72′, each which has avertical extent 78 that remains within an interior of the bulkcrystalline material 70 between the first surface 74 and an opposingsecond surface 80. In certain embodiments, the bulk crystalline material70 comprises bulk SiC where the first surface 74 comprises a carbon faceof the bulk crystalline material 70 and the second surface 80 comprisesa silicon face of the bulk crystalline material 70. As illustrated, thefirst subsurface laser damage pattern 72 may be formed with a nonlinearshape. In particular, the first subsurface laser damage pattern 72 isillustrated with a curved shape within the bulk crystalline material 70.In this manner, when the bulk crystalline material 70 is separated alongthe first subsurface laser damage pattern 72, a shape of the siliconface of the resulting SiC wafer will at least partially be defined bythe first subsurface laser damage pattern 72. For example, the curvedshape of the first subsurface laser damage pattern 72 may provide arelaxed positive bow from the silicon face of the resulting SiC wafer.

FIG. 12 is a cross-sectional schematic view of the bulk crystallinematerial 70 of FIG. 11 following formation of a second subsurface laserdamage pattern 82 centered at a different depth and registered with thefirst subsurface laser damage pattern 72, wherein a vertical extent 84of the second subsurface laser damage pattern 82 overlaps with thevertical extent 78 of the first subsurface laser damage pattern 72 in adamage overlap region 86. In certain embodiments, subsequent fracturingof the bulk crystalline material 70 may be performed along or throughthe damage overlap region 86 to at least partially form a SiC wafer witha relaxed positive bow from the silicon face. In certain embodiments,additional manufacturing steps, such as grinding or polishing, may beapplied to the first surface 74 after separation to provide a resultingSiC wafer where both the silicon face and the carbon face comprisesimilar nonlinear shapes.

In certain embodiments, subsurface laser damage lines may be formed atdifferent depths in a substrate without being registered with other(e.g., previously formed) subsurface laser damage lines and/or withoutvertical extents of initial and subsequent laser damage beingoverlapping in character. In certain embodiments, an interspersedpattern of subsurface laser damage may include groups of laser lineswherein different groups are focused at different depths relative to asurface of a substrate. In certain embodiments, a focusing depth ofemissions of a laser within the interior of the substrate differs amongdifferent groups of laser lines (e.g., at least two different groups offirst and second groups, first through third groups, first throughfourth groups, etc.) by a distance in a range from about 2 μm to about 5μm (i.e., about 2 μm to about 5 μm). After forming the subsurface laserdamage within a bulk crystalline material, a fracturing process asdisclosed herein (e.g., cooling a CTE mismatched carrier, application ofultrasonic energy, and/or application of mechanical force) is applied tofracture the bulk crystalline material along the subsurface laser damageregion, causing a crystalline material portion to be separated from aremainder of the bulk crystalline material.

FIG. 13 is a cross-sectional schematic view of a portion of bulkcrystalline material 92 showing subsurface laser damage 94 withsuperimposed dashed lines identifying an anticipated kerf loss materialregion 104. The anticipated kerf loss material region 104 includes thesubsurface laser damage 94, plus material 106 to be mechanically removed(e.g., by grinding and polishing) from a lower face or surface 108(e.g., silicon-terminated face) of a crystalline material portion 102(e.g., SiC wafer) to be separated from the bulk crystalline material 92,plus material 109 to be mechanically removed (e.g., by grinding andpolishing) from a surface 90A (e.g., carbon-terminated face) of aremainder of the bulk crystalline material 92A. The lower face orsurface 108 of the crystalline material portion 102 opposes a first faceor surface 90 thereof. In certain embodiments, the entire kerf lossmaterial region 104 may have a thickness that is less than 250 μm forSiC.

FIG. 14 is a cross-sectional schematic view of a portion of the bulkcrystalline material 92 showing curved subsurface laser damage 94 withsuperimposed dashed lines identifying the anticipated kerf loss materialregion 104. As illustrated, the subsurface laser damage 94 is arrangedwith a nonlinear (e.g. curved) profile across the bulk crystallinematerial 92 to provide a SiC wafer with a relaxed positive bow afterseparation. After separation, one or more surfaces of the SiC wafer aswell as surfaces of the remaining bulk crystalline material 92 may besubjected to polishing or grinding to remove damage associated with theseparation process. In certain embodiments, the anticipated kerf lossmaterial region 104 may be similar to planar configurations illustratedin FIG. 13. As such, the entire kerf loss material region 104 may have athickness that is less than 250 μm for SiC. Whereas wire sawing of SiCwafers typically entails kerf losses of at least about 250 μm perindividual wafer separated from a bulk crystalline material, laser- andcarrier-assisted separation methods disclosed herein and applied to SiCmay achieve kerf losses of less than 250 μm; or less than 175 μm; or ina range including 100 to 250 μm; or in a range including 80 to 250 μmper wafer; or in a range including 80 to 140 μm per wafer. Inparticular, for SiC wafers with imposed shapes, conventional methodstypically involve wire cutting thicker portions of SiC material andsubsequently forming a desired shape with grinding, polishing, or othermechanical material removal processes. According to embodimentsdisclosed herein, SiC wafers may be separated from bulk crystallinematerial 90 with imposed shapes at least partially determined by theshape of the subsurface laser damage 94 and the subsequent separationprocess while providing desirably low kerf losses.

According to embodiments disclosed herein, subsurface laser damage withvarious nonlinear profiles or shapes, including curved, may be providedwithin bulk crystalline material in a variety of manners. In certainembodiments, a laser power used to form the subsurface laser damage maybe variably applied across bulk crystalline material to form curvedsubsurface laser damage. In other embodiments, a focal point or heightof a laser used to form the subsurface laser damage may be variablyadjusted across the crystalline material to form curved subsurface laserdamage. In still other embodiments, a bulk crystalline material may beformed with a variable doping profile that alters laser absorptionacross the bulk crystalline material. In particular, a dopingconcentration may be formed that is generally higher at a center of thebulk crystalline material than at a perimeter of the bulk crystallinematerial. As subsurface laser damage is formed, laser absorptiondifferences due to changes in the doping concentration may form curvedsubsurface laser damage. In certain embodiments, methods may compriseone or more combinations of variable laser power, variable laser focalpoint or height, and variable doping profiles of the bulk crystallinematerial to form shaped subsurface laser damage regions.

FIG. 15 is cross-sectional schematic view of laser emissions 61 withvariable laser power being focused across a portion of the bulkcrystalline material 92 to form a curved shape 110 of subsurface laserdamage. As illustrated, the laser emissions 61 are configured with afirst laser power P1 near a perimeter of the bulk crystalline material92 and a second laser power P2 near a center of the bulk crystallinematerial 92. In certain embodiments, the second laser power P2 isconfigured to be greater than the first laser power P1, thereby formingdeeper subsurface laser damage in regions of the bulk crystallinematerial 92 that are registered with the second laser power P2. Whileonly two laser powers P1, P2 are illustrated in FIG. 15, any number oflaser powers may be provided across the bulk crystalline material 92 toform the curved shape 110 of subsurface laser damage. Depending on thelaser tool, targeted wafer thickness and the material properties of thebulk crystalline material, the average laser power may be configured tovary in a range including 2 W to 6 W or in a range including 3 W to 5.5W. In certain embodiments, higher or lower power ranges may be used.Additionally, the curved shape 110 of subsurface laser damage isillustrated in FIG. 15; however, other shapes of subsurface laser damagemay be formed depending on how the laser power is varied across the bulkcrystalline material 92.

FIG. 16 is cross-sectional schematic view of laser emissions 61 withvariable height adjustment being focused across a portion of the bulkcrystalline material 92 to form the curved shape 110 of subsurface laserdamage. As illustrated, the laser emissions 61 are configured withheights (e.g., “Z” position of the laser focal point) that vary from afirst laser height Z1 near a perimeter of the bulk crystalline material92 and a second laser height Z2 near a center of the bulk crystallinematerial 92. In certain embodiments, the second laser height Z2 isconfigured to provide deeper subsurface laser damage in the bulkcrystalline material 92 than the first laser height Z1. The variablelaser heights Z1, Z2 may be provided by adjusting the laser focal pointposition Z relative to the surface of the bulk crystalline material 92and/or optical elements within the laser lens to move the focal point tothe targeted depth for formation of subsurface laser damage in the bulkcrystalline material 92. While the curved shape 110 of subsurface laserdamage is illustrated in FIG. 16, other shapes of subsurface laserdamage may be formed depending on how the laser height or focal point isvaried across the bulk crystalline material 92.

FIG. 17 is cross-sectional schematic view of laser emissions 61 beingfocused across a variably doped portion of the bulk crystalline material92 to form the curved shape 110 of subsurface laser damage. A simpledoping profile plot is provided below the cross-sectional schematic viewof the bulk crystalline material 92. The y-axis represents the relativedoping concentration (ccn) within the bulk crystalline material 92 whilethe x-axis represents lateral position of the bulk crystalline material92. As illustrated, the doping of the bulk crystalline material 92 isconfigured to have a radial doping profile that is higher near a centerof the bulk crystalline material 92 and lower near a perimeter of thebulk crystalline material 92. Accordingly, as the laser emissions 61 arepassed along the bulk crystalline material 92, the laser emissions 61may exhibit laser absorption levels that vary with respect to horizontalposition within the bulk crystalline material 92, thereby forming thecurved shape 110 of subsurface laser damage. The variable doping profileof the bulk crystalline material 92 may be provided during crystalgrowth of the bulk crystalline material 92. In certain embodiments, thebulk crystalline material 92 is arranged with a center doping ring ofhigher doping concentration. While the curved shape 110 of subsurfacelaser damage is illustrated in FIG. 17, other shapes of subsurface laserdamage may be formed depending on how the doping profile is arrangedwithin the bulk crystalline material 92.

FIGS. 18-21 illustrate various views of bulk crystalline materialshaving variable doping profiles. FIG. 18 is a side cross-sectionalschematic view of bulk crystalline material 92 of SiC on a seed crystal112, showing a cylindrically shaped higher doping region 114 extendingupward from the seed crystal 112 through the entire thickness of thebulk crystalline material 92 along a central portion thereof. In certainembodiments, the higher doping region 114 is laterally bounded by alower doping region 116 that is arranged along a perimeter of the bulkcrystalline material 92. In certain embodiments, the lower doping region116 may be intentionally doped, unintentionally doped, or undoped.Although FIG. 18 shows the size (e.g., width or diameter) of the higherdoping region 114 as being substantially constant throughout thethickness of the bulk crystalline material 92, the size of a dopingregion can vary with vertical position within the bulk crystallinematerial 92 (e.g., typically being larger in width or diameter closer toa seed crystal, and smaller with increasing distance away from the seedcrystal). Additionally, a magnitude of doping within the higher dopingregion 114 can vary with vertical position in the bulk crystallinematerial 92. A thin cross-sectional portion 118 of the bulk crystallinematerial 92 is indicated in dashed lines and may define a SiC wafer 120,as shown in FIG. 19. FIG. 19 is a top schematic view of the SiC wafer120 derived from the bulk crystalline material 92 of FIG. 18 along thecross-sectional portion 118. As illustrated, the higher doping region114 forms a circular shape within the perimeter of the ring-shaped lowerdoping region 116 of the SiC wafer 120. In such embodiments, a variablesubsurface laser damage region may be provided along the cross-sectionalportion 118 of FIG. 18 to provide the SiC wafer 120 with a relaxedpositive bow as previously described.

FIG. 20 is a side cross-sectional schematic view of bulk crystallinematerial 92 of SiC on the seed crystal 112, showing a frustoconicallyshaped higher doping region 114 extending upward from the seed crystal112 through the entire thickness of the bulk crystalline material 92along a central portion thereof. In certain embodiments, the lateralposition and shape of the higher doping region 114 can differ relativeto the configuration shown in FIG. 20 if a vicinal (e.g., offcut at anangle non-parallel to c-plane) seed crystal is used for growth of thebulk crystalline material 92. For example, if a vicinal seed crystal isused, then the higher doping region 114 may be more oval than round inshape, and/or may be offset laterally relative to a center of the bulkcrystalline material 92. FIG. 21 is a side cross-sectional schematicview of bulk crystalline material 92 of SiC on the seed crystal 112,showing a frustoconically shaped higher doping region 114 extendingupward from the seed crystal 112 at a non-centered position relative toa center of the seed crystal 112 and upward through the entire thicknessof the bulk crystalline material 92. In FIG. 21, the seed crystal 112may comprise a vicinal (e.g., offcut) seed crystal and the higher dopingregion 114 may form a generally oval shape when viewed from above. As isevidenced by the variable shapes of the higher doping regions 114 ofFIGS. 20 and 21, lateral dimensions of the higher doping region 114 andthe lower doping region 116 can vary depending on vertical positionwithin the bulk crystalline material 92. In this manner, in order touniformly produce multiple SiC wafers having the same relaxed positivebow, laser conditions (e.g., one or more of the focal point height andthe laser power) used to form subsurface laser damage regions may needto be altered to compensate for the vertical changes in the higher andlower doping regions 114, 116.

FIG. 22 is a side cross-sectional schematic view of a SiC wafer 122 witha relaxed positive bow according to embodiments disclosed herein. TheSiC wafer 122 includes a silicon face 124 and an opposing carbon face126. As illustrated, the SiC wafer 122 is formed with a relaxed positivebow from the silicon face 124 according to previously describedfabrication techniques. Notably, the carbon face 126 is formed with asimilar or parallel shaped bow. In certain embodiments, combinations ofone or more of laser subsurface damage and subsequent grinding orpolishing may form such corresponding shapes of the silicon face 124 andthe carbon face 126. A theoretical flat wafer 128 is superimposed on theSiC wafer 122 with dashed lines. The amount of relaxed positive bow ofthe silicon face 124 may be quantified by a distance or deviation 130 ata highest point (e.g., the center in FIG. 22) of the silicon face 124 ascompared with a silicon face 124′ of the theoretical flat wafer 128without the influence of gravity. In a similar manner, bow of the carbonface 126 may be quantified as a distance or deviation from a carbon face126′ of the theoretical flat wafer 128.

FIG. 23 is a side cross-sectional schematic view of a SiC wafer 132 witha relaxed positive bow according to embodiments disclosed herein. TheSiC carbide wafer 132 includes the silicon face 124 and the opposingcarbon face 126. As illustrated, the SiC wafer 132 is formed with arelaxed positive bow from the silicon face 124 according to previouslydescribed fabrication techniques, while the carbon face 126 is formedwith a generally planar profile. In this manner, a profile of thesilicon face 124 that is defined by the relaxed positive bow differsfrom the profile of the carbon face 126 such that the SiC wafer 132comprises local thickness variation from a perimeter of the SiC wafer132 to a thicker central portion of the SiC wafer 132. In certainembodiments, combinations of one or more of laser subsurface damage andsubsequent grinding or polishing may form such shapes of the siliconface 124 and the carbon face 126. As described for FIG. 22, the amountof relaxed positive bow of the silicon face 124 may be quantified by thedistance or deviation 130 at a highest point of the silicon face 124 ascompared with the silicon face 124′ of the theoretical flat wafer 128without the influence of gravity.

Various techniques may be used to measure amounts of relaxed positivebow of wafers according to embodiments disclosed herein. Such techniquesinclude arrangements to correct for gravity-induced deformation orsagging of wafers. One such measurement technique, as described in theSemiconductor Equipment and Materials International (SEMI) standardMF1390 titled “Test Method for Measuring Warp on Silicon Wafers byAutomated Non-Contact Scanning,” is used to correct for gravitationaleffects by comparing first wafer measurements with inverted second wafermeasurements such that the difference between the two corresponds togravitational effects. Other measurement techniques may be found in SEMIstandard 3D4-0915 titled “Guide for Metrology for Measuring Thickness,Total Thickness Variation (TTV), Bow, Warp/Sori, and Flatness of BondedWafer Stacks,” which describes various gravity compensation techniquesfor horizontally and vertically supported wafers. In certainembodiments, such measurement techniques may include interferometry. Incertain embodiments, measurement techniques may include the use of anoptical flat that is used to determine flatness, or lack thereof, ofwafers.

FIGS. 24A-24C are side cross-sectional schematic view of the SiC wafer122 of FIG. 22 during measurements to quantify relaxed positive bowwhile correcting for gravitational effects. FIG. 24A is a sidecross-sectional schematic view of the SiC wafer 122 of FIG. 22 thatforms a relaxed positive bow from the silicon face 124, opposite thecarbon face 126 without gravitational effects. In FIG. 24B, the SiCwafer 122 is arranged on an edge support 134 for wafer bow or warpcharacterization. In certain embodiments, the edge support 134 isarranged in a manner to approximate how the SiC wafer 122 may besupported during subsequent device fabrication processes, includedepitaxial growth of thin films on the SiC wafer 122. The edge support134 may comprise any number of configurations, including a three-pointsupport, a four-point support, or a continuous ring for support. Asillustrated, when the SiC wafer 122 is arranged on the edge support 134,gravitational effects can cause the SiC wafer 122 to deform, bow, or sagin a direction from the silicon face 124 toward the carbon face 126.Notably, with the influence of gravity, the relaxed positive bow asillustrated in FIG. 24A can form a flattened, or even convex shape ofthe silicon face 124. Such a configuration may be desirable forproviding improved temperature uniformity of the SiC wafer 122 duringepitaxial device growth as previously described. In FIG. 24C, the SiCwafer 122 is flipped or inverted such that the silicon face 124 isoriented down toward the edge support 134 and the carbon face 126 isoriented up. As illustrated, gravitational effects can cause the SiCwafer 122 to deform, bow or sag a greater amount than what is shown inFIG. 24B. In this regard, wafer bow or warp characterizationmeasurements may be taken from both the silicon face 124 and the carbonface 126 of the SiC wafer 122 and compared to compensate for thegravitational effects. For example, if the measured amount of saggingfrom the silicon face 124 (e.g., FIG. 24B) is equal to the measuredamount of sagging from the carbon face 126 (e.g., FIG. 24C), then theSiC wafer 122 may be characterized as generally flat or having norelaxed positive bow. Accordingly, if the measured amount of saggingfrom the silicon face 124 (e.g., FIG. 24B) is less than the measuredamount of sagging from the carbon face 126 (e.g., FIG. 24C), then theSiC wafer 122 may be characterized as having a relaxed positive bow thatis quantifiable as the difference between the two measurements and iscompensated for gravitational effects during measurement.

FIG. 25 is a side cross-sectional schematic view of the SiC wafer 122 ofFIG. 22 during vertically-oriented measurements to quantify relaxedpositive bow. As illustrated, the SiC wafer 122 is vertically arrangedon an optical flat 136 for characterization. During flatnessmeasurements, the optical flat 136 and the SiC wafer 122 are illuminatedwith light 138, such as monochromatic light or white light, amongothers, and interference fringes are formed that are used to quantifyflatness of the SiC wafer 122 relative to the optical flat 136. As theSiC wafer 122 is vertically oriented during characterization,gravitational effects are reduced.

In certain embodiments a relaxed positive bow is in a range from greaterthan 0 μm to 50 μm, or in a range from greater than 0 μm to 40 μm, or ina range from greater than 0 μm to 25 μm, or in a range from greater than0 μm to 15 μm, or in a range from greater than 0 μm to 10 μm, or in arange from 5 μm to 50 μm. For certain applications, a relaxed positivebow of greater than 50 μm may result in wafers that maintain a positivebow during subsequent fabrication steps, such as epitaxial growth, thatcan have a negative effect on device uniformity. As previouslydescribed, SiC wafers as disclosed herein may comprise a diameter of atleast 100 mm, at least 150 mm, at least 200 mm or greater, or in a rangeincluding 150 mm to 205 mm and a thickness in a range of 100 to 1000 μm.In certain embodiments a SiC wafer comprises a diameter to thicknessratio of at least 250; or at least 300; or at least 400; or in a rangeincluding 250 to 1020. In certain examples, a 6 inch (152.4 mm) SiCwafer comprises a thickness of 200 μm (0.2 mm) for a diameter tothickness ratio of 762; or a thickness of 350 μm (0.35 mm) for adiameter to thickness ratio of 435 (rounded); or a thickness of 500 μm(0.5 mm) for a diameter to thickness ratio of 305 (rounded). In otherexamples, an 8 inch (203.2 mm) SiC wafer comprises a thickness of 200 μm(0.2 mm) for a diameter to thickness ratio of 1016; or a thickness of500 μm (0.5 mm) for a diameter to thickness ratio of 406 (rounded); or athickness of 800 μm (0.8 mm) for a diameter to thickness ratio of 254.Each of the 6 inch and 8 inch SiC wafer examples above may be arrangedwith a relaxed positive bow according to embodiments described above. Incertain embodiments, the amount of relaxed positive bow may be arrangeddifferently based on wafer diameter and thickness dimensions. In oneexample, a 6 inch (152.4 mm) SiC wafer with a thickness of 350 μm (0.35mm) may comprise a relaxed positive bow in a range including 8 μm to 16μm to compensate for sagging, warping, or other deformation effects. Fora same wafer thickness, relaxed positive bow may be increased withincreasing wafer diameter. For example, an 8 inch (203.2 mm) SiC waferwith a thickness of 350 μm (0.35 mm) may comprise a relaxed positive bowin a range including 30 μm to 50 μm to compensate for sagging, warping,or other deformation effects. For a same wafer diameter, relaxedpositive bow may be decreased with increasing wafer thickness. Forexample, an 8 inch (203.2 mm) SiC wafer with a thickness of 500 μm (0.5mm) may comprise a relaxed positive bow in a range including 10 μm to 30μm, and an 8 inch (203.2 mm) SiC wafer with a thickness of 800 μm (0.8mm) may comprise a relaxed positive bow in a range including 4 μm to 12μm to compensate for sagging, warping, or other deformation effects. Incertain embodiments, other relaxed positive bow ranges are possible,depending on the material type, and/or material dimensions (e.g.,thickness and diameter), and/or crystalline stress that may be present.In this regard, large area SiC wafers with thicknesses described aboveare disclosed with relaxed positive bow, thereby reducing sagging,warping, or other deformation effects associated with gravitationalinfluence or from preexisting crystal stress for SiC wafers with suchdimensions.

As noted previously herein, progressively higher laser power levels maybe necessary for formation of laser damage sufficient to partcrystalline material by fracturing, starting at a position distal fromthe seed crystal and obtaining wafers at cross-sectional positionsprogressively approaching the seed crystal. Use of high laser power ateach sequential depth position when forming subsurface damage wouldentail unnecessary material loss, and would also significantly increasewafer-to-wafer thickness spread due to variability in both the damagedepth and the point at which decomposition is reached relative to alaser beam waist. Such concept may be understood with reference to FIGS.26 and 27.

FIG. 26 is a schematic side cross-sectional view of a conventional laserfocusing apparatus that focuses an incoming horizontal beam 400 in apropagation direction with a lens 404, forming an outgoing beam 402having a beam waist pattern having a minimum width W_(f) at a position406 corresponding to a focal length f of the lens 404. Downstream ofthis position 406, the beam width broadens to a wider region 408. FIG.27 is a schematic side cross-sectional view of a vertically orientedfocused laser beam 402 that may be directed into a crystalline materialand exhibits a beam waist pattern (with a minimum width at a position406 corresponding to a focal length of a lens (not shown)), with thebeam width broadening thereafter to a wider region 408. When the focusedlaser beam 402 is directed within a bulk crystalline material, thecrystalline material will thermally decompose at different thresholdpoints (i.e., depths) depending on factors such as laser power, degreeof absorption of radiation by the crystalline material (which may beinfluenced by presence or absence of dopants and/or crystal defects thatmay vary with depth (and width) position within the substrate), anddegree of focusing which is dependent on vertical position. Threedifferent decomposition threshold points 410A-410C are shown in FIG. 27.

Methods and apparatuses disclosed herein permit the foregoing issues tobe addressed by imaging a top surface of a crystalline material havingsubsurface laser damage to detect uncracked regions, analyzing one ormore images to identify a condition indicative of presence of uncrackedregions within the crystalline material, and taking one or more actionsresponsive to the analyzing (e.g., upon attainment of appropriateconditions). Such actions may include performing an additional laserpass at the same depth position and/or changing an instruction set forproducing subsurface laser damage at subsequent depth positions. Suchmethods and apparatuses facilitate production of substrate or waferportions with imposed shapes and without unnecessary material loss.

Technical benefits that may be obtained by one or more embodiments ofthe disclosure may include: formation of wafers with relaxed positivebow from device faces and reduced crystalline material kerf lossescompared to conventional techniques; reduced processing time andincreased throughput of crystalline material wafers and resultingdevices; and/or increased reproducibility of thin wafers with relaxedpositive bow that are separated from bulk crystalline material.

Those skilled in the art will recognize improvements and modificationsto the preferred embodiments of the present disclosure. All suchimprovements and modifications are considered within the scope of theconcepts disclosed herein and the claims that follow.

What is claimed is:
 1. A crystalline material processing method comprising: providing a bulk crystalline material comprising silicon carbide (SiC); forming a subsurface laser damage pattern within the bulk crystalline material by variably adjusting at least one of a laser power and a laser focal point to form a nonlinear profile of the subsurface laser damage pattern from a perimeter of the bulk crystalline material to a center of the bulk crystalline material; and separating a SiC wafer from the bulk crystalline material along the subsurface laser damage pattern.
 2. The crystalline material processing method of claim 1, wherein the nonlinear profile forms a curved shape from the perimeter of the bulk crystalline material to the center of the bulk crystalline material.
 3. The crystalline material processing method of claim 1, wherein the laser power is variably adjusted such that the laser power is different along the perimeter of the bulk crystalline material than at the center of the bulk crystalline material.
 4. The crystalline material processing method of claim 3, wherein the laser power is greater at the center of the bulk crystalline material than along the perimeter of the bulk crystalline material.
 5. The crystalline material processing method of claim 1, wherein the laser power is variably adjusted in a range including 2 watts (W) to 6 W.
 6. The crystalline material processing method of claim 1, wherein the laser focal point is variably adjusted such that a height position of the laser focal point is different along the perimeter of the bulk crystalline material than at the center of the bulk crystalline material.
 7. The crystalline material processing method of claim 6, wherein the height position of the laser focal point is configured deeper into the bulk crystalline material at the center of the bulk crystalline material than along the perimeter of the bulk crystalline material.
 8. The crystalline material processing method of claim 1, wherein forming the subsurface laser damage pattern within the bulk crystalline material comprises variably adjusting the laser power and the laser focal point to form the nonlinear profile of the subsurface laser damage pattern.
 9. The crystalline material processing method of claim 1, wherein the bulk crystalline material comprises a radial doping profile that is variable from the perimeter of the bulk crystalline material to the center of the bulk crystalline material.
 10. The crystalline material processing method of claim 9, wherein the radial doping profile comprises a lower doping region near the perimeter of the bulk crystalline material and a higher doping region that is closer to the center of the bulk crystalline material than the perimeter of the bulk crystalline material.
 11. The crystalline material processing method of claim 10, wherein the higher doping region is positioned at the center of the bulk crystalline material.
 12. The crystalline material processing method of claim 10, wherein the higher doping region is positioned offset from the center of the bulk crystalline material.
 13. The crystalline material processing method of claim 1, wherein the subsurface laser damage pattern comprises a plurality of subsurface laser damage lines formed at different depths within the bulk crystalline material.
 14. The crystalline material processing method of claim 13, wherein the plurality of subsurface laser damage lines are formed at different depths in a range including 2 microns (μm) and 5 μm.
 15. The crystalline material processing method of claim 13, wherein the plurality of subsurface laser damage lines are formed non-perpendicular to a [1120] crystal direction of SiC.
 16. The crystalline material processing method of claim 1, wherein the SiC comprises 4-H SiC.
 17. The crystalline material processing method of claim 1, wherein the SiC comprises off-axis 4-H SiC in a range including 0.5 degrees to 10 degrees from a c-axis of the SiC.
 18. The crystalline material processing method of claim 1, wherein the SiC comprises on-axis 4-H SiC.
 19. The crystalline material processing method of claim 1, wherein the SiC wafer forms a relaxed positive bow from a silicon face of the SiC wafer.
 20. The crystalline material processing method of claim 19, wherein the relaxed positive bow is in a range from greater than 0 microns (μm) to 15 μm.
 21. The crystalline material processing method of claim 19, wherein the relaxed positive bow is in a range including 30 microns (μm) to 50 μm.
 22. The crystalline material processing method of claim 19, wherein the relaxed positive bow is in a range including 8 microns (μm) to 16 μm.
 23. The crystalline material processing method of claim 1, wherein the SiC wafer comprises a diameter to thickness ratio of at least
 250. 24. The crystalline material processing method of claim 1, wherein the SiC wafer comprises a diameter to thickness ratio of at least
 300. 25. The crystalline material processing method of claim 1, wherein the SiC wafer comprises a diameter to thickness ratio of at least
 400. 26. The crystalline material processing method of claim 1, wherein the SiC wafer comprises a diameter to thickness ratio in a range including 250 to
 1020. 27. The crystalline material processing method of claim 1, wherein a kerf loss associated with forming the SiC wafer from the bulk crystalline material is less than 250 microns (μm).
 28. The crystalline material processing method of claim 27, wherein the kerf loss is in a range including 100 μm to 250 μm.
 29. The crystalline material processing method of claim 27, wherein the kerf loss is less than 175 μm.
 30. The crystalline material processing method of claim 1, wherein the SiC wafer forms a relaxed positive bow from a silicon face of the SiC wafer, and a carbon face of the SiC wafer comprises a shape that corresponds to the relaxed positive bow from the silicon face.
 31. The crystalline material processing method of claim 1, wherein the SiC wafer comprises a diameter that is in a range from 150 millimeters (mm) to 205 mm. 